The term 'vocal music' says it all for me
It's a long tome since I read Bruno Netl's 'Primitive Music' and John Blacking's 'How Musical is Man' which were both influential in persuading me that the voice was man's first musical instrument - time I read them again, I think
'Click music' and mimicking animals for food gathering (like imitating bees for honey-gathering) - are very early examples of the voice being used as a musical instrument
More recently, the voice being used to produce music for dancing when there are no musical instruments available, or in Scotland for retaining the subtleties of tunes.
The voice is basically a tool used to communicate ideas - once you use it for something else it becomes what it is used for
This is basically a philosophical point, same as - if you are caught in flood and turn a table upside down to escape, does it become a boat?
Jim Carroll